5 ms·

> What happens when a GPS satellite fails? The receivers use other satellites. They have to anyway: You can't get a fix with only one satellite.

• baddox 13y ago
  I would imagine you normally need three. If I'm visualizing the geometry correctly, the intersection of three spheres is two points, and it should be easy to guess which of the two is the more likely location of your device.
  • mutagen 13y ago
    Because relatively cheap GPS receiver clocks drift, typically 4 satellites are needed for a position. You can assume an elevation, especially at sea level, and solve a position with three satellites but this introduces other factors (ellipsoid vs geoid, satellite constellation geometry, etc) that can make a good position difficult to obtain. In practice there are enough satellites that these considerations are theoretical. Most situations that would involve limited satellites also introduce stuff like multi path reflections that further degrade position accuracy.
    • tinkerdol 13y ago
      Here is a graphic to add to that explanation if anyone is curious: http://gis.stackexchange.com/questions/12866/why-does-gps-positioning-require-four-satellites http://gis.stackexchange.com/questions/12866/why-does-gps-po...
  • avn2109 13y ago
    In North America your GPS probably connects to between five and twelve satellites.